Snap acting thermal device



FIG. 3.

May 21, 1935.

FIG. 2;

E, O. BLQDGETT SNAP ACTING THERMAL DEVICE Filed May 15, 1951 INSULA 0N ATTORNEY Patented May 21, 1935 PATENT OFFICE SNAP ACTING THERMAL DEVICE Edwin o. Blodgett, Rochester, N. Y., assignor a, General Railway Signal Company, Rochester,

ApplicationMay 1a, 1931, Serial No. 536.991 11 Claims. (01. 200-122) This invention relates .to time-element devices and more particularly to thermal-electric timeelement devices having definite snap action.

Thermal-electric time-element devices of the usual type employ a heating element to distort a thermostatic element and thereby function to operate contact means or the like. Such devices necessarily actuate such contact means very slowly which involves well known disadvantages in making or breaking circuits carrying a substantial amount of current or having a very great impressed voltage. These thermostatic elements also have a definite shape or position to which they automatically return after de-energization of the heating element. I

In view of the above, it is proposed, in accordance with this'invention, to provide a thermalelectric device which is operable to either 01' two retained positions and which has an inherent snap action after a definite period of energization.

Other objects, purposes and characteristic features of the present invention will appear as the description thereof progresses, during which references will be made to the accompanying drawing which shows the invention in a mannerto make it easily understood, rather than with the view of showing the particular construction prelerably employed in practice, and in which:-

Fig. 1 is a plan view of a device constructed according to this invention;

Fig. 2 is a sectional view on line 22 of Fig. I viewed in the direction indicated by the arrows; and

Fig. 3 is an elevational view of a modified device also embodying the present invention.

The thermal-electric device illustrated in the embodiment of the invention shown in Figs. 1 and 2, comprises two bi-metallic strips l and 2 each having one end secured to a movable member 8 and the other end to a fixed member l by suitable means such as rivets 5, as shown. The

member 3 is slidably attached to the member 4.

by suitable means such as the rivets i and 1 which pass through slots in the member I and are fixed in the member 4. The'heads oi the rivets i and 'l are arranged to retain the member 3 yet permit a slight linear motion of the member 3 on the member 4. i

The centers of the bi-metallic strips I and 2 are rigidly interconnected by a rod 8 preferably of insulating material and may be held by metal inserts 9 which pass through holes in the strips I and 2 and are threaded into the rod I. Similar insulating rods II and Il may also screw on the other ends of the inserts I to securely clamp the strips I and 2 and may also serve to operate contact means.

The member 3 is biased inwardly on the member l by a spring I2 which is held between the member 3 and an extension of the member 4 by '5 an adjustable screw I3 passing through a hole in the extension and being tapped into the memher 3. This biasing spring I2 is sufilciently strong to cause the strips l and 2 to buckle to a curved position either side of center, and the ex 10 tent of this buckling isadjusted by the screw I I which directly limits the inward motion of the member 3 on the member 4.

The bi-metallic strips l and '2 are constructed in the-conventional way by employing two metals 15 whose difierential expansion distorts the member when subjected to temperature changes. These strips l and 2 are oppositely arranged on the members 3 and, that is, so that like temperature changes tend to produce opposite directions of 20 distortions therein. These strips may, oi! course, be thus arranged in either of two ways but in this disclosure it will be considered that each strip has the metal or the greater coefllcient of expansion on the inside of the device in Fig. 1. Electri- 25 cal heating elements I4 and I! are wound each side of the center rod 8 over suitable material to electrically insulate the windings of the elements from the bi-metallic strips.- Each end of these elements may be connected to the device as shown and energy applied to the center of each element from individual circuits which use the strips or the metal frame of the device as a common connection thereto.

Considering that the strips I and- 2 have been buckled or biased to the position shown in Fig. 1, it is evident that the energization of the heating element I5 tends to warp the bi-metallic strip! to a straight position because the inside metal oi! this strip has the greater coefiicient of expansion 40 and obviously. tends to distort the strip in a direc tion opposite to the buckle produced by the biasing spring I2. This straightening oi the strip 2 alsostraightens the strip I through the connect- ,in Fig. 1 when they reach a slight beyond-center position. It is now obvious that the bi-metallic strips are retained in either of such extreme operated'positions by the biasing spring i2 until the energization of the opposite heating element.

This thermal electric device may be employed to operate various means but it has been illustrated as operating a spring contact arrangement and it is desired to be understood that this is shown only by way of illustrating-the utility of the device. A support it may be secured to the member d by suitable means such as by rivets H to thereby provide a contact mounting means.

The contact arrangement shown consists of movable resilient contact springs i8 operable by the rods 98 and H to engage with either front or back fixed resilient contact springs id at low resistance contact points. These fixed contact springs have rigid stops 20 assembled together with the contact springs 58 and 59 between insulating spacers 28 by through bolts 22 which have insulated body bushings and clamp the assembly to upstanding ends the support 06. Short insulated terminal str ps 23 and a strip 25 connected to the metal of the device may also be secured to the support it in a similar manner for terminating the leads from the heating elements M and is thereby facilitating in making external connections.

It will be noted in the device that the amount of buckle in the bi-metallic strips l and 2 is readily adjustable by the screw it which is threaded into the member- 3. The body of this screw is freely passes through an enlarged hole in the extension of the member 6 when the operation of the device actuates the member 3 but the enlarged head of the screw 63 engages the extension of the member Q to stop the biased inward motion of the member 3. It is obvious that the operation of such a device is unaffected by changes in temperature so long as both elements are of substantially the same temperature because the opposing arrangement of the bi-metallic strips produces only stress between the strips and no change in position thereof, relative to the frame of the device.

The modified form of the present invention illustrated in Fig. 3 has a single operating strip only and consequently is electrically operable to only one position. A manual operable means 26, which may be termed a manual reset, is secured to the strip 2 and arranged to pass through an enlarged slot in the member 3 and a suitable hole in the member 8 A contact arrangement similar to that of Fig. 1 is illustrated as being operated by the modified device but it is understood that this device is also applicable to operate various other functions as well.

The electrical operation of the device in Fig. 3 is accomplished by passing suflicient electrical current through the heating element I which distorts the bi-metallic strip 2 which is arranged with the metal of larger coeflicient of expansion on the inside or the same side as the manual reset 24. This causes the same operation of the strip 2 as was previously described and'the strip is then retained in a positionopposite to thatshown until manually reset by pressing the reset means 24.

It is ,also conte'mplated to construct a device similar to thatshown in Fig. 3 with the manual .reset 24 omitted and having a bi-metallicstrip this device would have an operating strip arranged as in Fig. 3 but with apermanent set in the curved shape shown when unbiased by the spring i2, and this permanent set would be-so adjusted to exert a greater force tending to return the strip, when at the normal temperature,

toits set shape than is exerted by the spring l2 tion after a predetermined length of time and may be arranged to either automatically return to its original condition a predetermined time after each operation or to retain such a position until returned either manually or by a reversed thermal-electric means.

The above description of the forms of the present invention is given solely by the way of example, and is not intended, in'any manner whatsoever, in a limiting sense. It is also to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice, without in any manner departing from thespir'it or scope of the present invention, except as limited by the appended claims.

Having thus described my invention, what I claim is: v I

1. In a thermal-electric device, two opposed thermo-responsive strips, a rigid support at each end of said strips, compression biasing means on said supports arranged to produce a longitudinal buckle in said strips, individual electrical heating elements associated with each strip and means rigidly interconnecting intermediate pertions of said strips.

2. In a thermal-electric device, two substantially parallel thermo-responsive elements oppo= sitely arranged with an intermediate rigid connection, end supports for said thermo-responsive elements having inward biasing means arranged to buckle said elements to a curved position and individual heating units for said thermo-sensitive elements.

8. In a thermal-electric device, two longitudinally resilient supporting members, two spring, bi-metallic strips arranged to longitudinally spread said supporting members when straight, said bimetallic strips being arranged in parallel and opposite relation and having an intermediate interconnection.

4., In combination, two substantially fixed supports, two oppositely arranged bi-metallic strips held between said two fixed supports and having a length greater than the distance between said two supports, means heating one or the other of said bi-metallic strips whereby said, bi-metallic tions of 'the strips,- a memberinterconnecting the one end of the strips, a second member connecting the-other ends of the strips and arranged to move longitudinally with respect to each other,

a springbiasing said second member toward said first member whereby said bi-metallic strips are biased to either of two curved positions, an adjustable means limiting the inwardly biased position of said second member, an electric heating element associated with one 0! said strips for operating both strips to one of said curved posi-- tions, a similar element on the other of said strips for operating both strips to the other oi! said curved positions and contact means operated in accordance with the curved positions or said strips.

6. In a thermal-electric relay, a bi-metallic strip, a member carrying one end of said strip,

a second member carrying the other end of said strip and guided for motion longitudinally on said first member, a spring inwardly biasing said second member on said first member whereby said bi-metallic strip is buckled to a curved position to either side of center, an adjustable stop for said inwardly biased movement of said second member, an electric heating element arranged to warp said bi-metallic strip to a curved position one side of center, a manually operable means for positioning said strip the other side of center and contact means operated in accordance with the position of said strip.

nection, and supports for said thermo-re'sponsive elements arranged to buckle said elements to a curved position and individual heating units for said thermo-sensitive elements.

9. In combination, two supports, two oppositely arranged bi-rnetallic strips held between said two supports and having a length greater than the distance between said two supports, means heating one or the other of said bi-metallic strips whereby said bi-metallic strips are operated to either of two positions and means operated in accordance with the two positions 01 said bi metallic strips.

10. In a thermal-electric device, a thermo-re- I sponsive strip, a first support at one end of the of said strip to permit manual operation of the 

